Hybrid systems for application in vehicles are anticipated in a number of designs from the prior art. What is common to all such systems is that in the drive train at least two different engines/aggregates are provided, through which the drive can occur selectively or jointly, wherein at least one of the engines is suitable as an engine in a first mode of operation and in a second mode of operation as a machine for converting the braking energy into another form of energy for the purpose of temporary storage and/or for powering other consumers. In the application in vehicles, the first engine is often executed as an internal combustion engine, whereas the second engine is executed as an electric machine that is suitable to feed electric energy into an accumulator whilst in generator operation. Such a hybrid system, for instance, is depicted in the prior publication DE 103 10 831 A1, FIG. 30; this discloses a power transmission device that is disposed between at least two engines and a downstream-disposed consumer in the form of a transmission. For full decoupling of the first engine from the drive train, a device for disconnection/connection of the power flow is provided at least between this and the power transmission device, which is executed in the form of a selectable clutch device, which is designated also as engine clutch or separating clutch. The second engine is designed as an electric machine by which the armature is connected non-rotatably with the power transmission unit. The power transmission device comprises at least a start-up element, preferably a hydrodynamic component, and in this case, it comprises a device at least for partially bypassing the power flow by means of the hydrodynamic component. The downstream-disposed transmission that is generally executed as manual-shift transmission is characterized by a plurality of hydraulic-medium-actuated shifting elements. To guarantee the hydraulic medium supply for the power transmission device and transmission shifting elements, appropriate operating-and-control fluids supply and/or guidance system is provided, comprising at least a hydraulic circulation system in which the required operating fluid with appropriate pressure is supplied by means of a pumping device in the form of a so-called transmission oil pump. The transmission oil pump is furthermore required for the operation of separation and/or start-up clutch/clutches. For this, the transmission oil pump for safe operation is preferably connected directly with the input of the power transmission device. This coupling allows driving in different modes of operation of the drive train by means of the first and/or second engine.
The following modes of operation are differentiated in traction operation as possible basic modes of operation of such a drive train and can be modified by further subsidiary modes of operation. First, driving, particularly powered driving with power flow from the first engine, in particular internal combustion engine with a closed device for disconnection/connection of the power flow between at least the first engine and the power transmission device, in particular by means of a first and/or second power branch of the power transmission device. Second, driving, particularly electric driving with power flow from the second engine, in particular electric machine, by means of a first and/or second branch of the power transmission device with an opened/closed device for disconnection/connection of the power flow between at least the first engine and the power transmission device.
The emergency operation is characterized by exclusive operation of the first engine that is started by means of its own starting motor.
A critical disadvantage of such a system is that in conventional hydraulic systems used for this purpose while the vehicle is stationary, for instance during short standstill, the transmission oil pump can run empty due to drive outage. When starting up anew, first the hydraulic supply and hence the transmission oil pump must be driven, which again must provide sufficient pressure and volumetric flow so that the required servo units to be pressurized and the hydrodynamic component are filled as well. Since this leads to substantial delays in the reaction to the accelerator actuation, which under certain circumstances in a variety of situations also poses a significant safety risk, the possibility exists that, also in a stationary vehicle, the hydraulic system of the transmission must be kept filled with low-pressure hydraulic media volume. The transmission oil pump being used must be able to replenish, in particular, the leakages of the hydraulic system while the vehicle is stationary. To guarantee this, an additional electrically driven oil pump is often used in the prior art. Alternatively, the electric machine of the hybrid system and the already existing main transmission oil pump is used, which is associated with technical disadvantages. Thus, an additionally provided and electrically driven oil pump entails extra expenses. On the other hand, not using such an ancillary pump is also characterized by a plurality of disadvantages. If the clutch device is open in the pressure-less state, in one of such embodiments, the emergency operation characteristics are no longer guaranteed. Even when the internal combustion engine is started by means of an ancillary starter motor, no oil pressure can be developed inside the transmission, since the pressure-less open-clutch device cannot be closed so that the transmission oil pump is driven. If the mode of operation of the transmission, for instance, is disturbed owing to a control error and must be operated in an emergency mode, then even an existing electric ancillary pump cannot be used, since it is also activated by the transmission control system.
Furthermore, it is required in the “electric driving” state that the selectable clutch device between at least the first engine and the power transmission device is fully open, in order to avoid drag losses through the elements carrying and/or forming frictional surfaces that rotate relative to one another. In the process, in this operating range in most cases, the required minimum pressure for fully opening the clutch is not at disposal. The use of a pressure-less closed-clutch requires very high-pressure levels for opening, whilst in the electric driving mode. This reduces the efficiency of the entire system.
A further combined power transmission and drive unit according to the prior art is known, for instance, from the German patent application DE 10 2006 040 117 A1. The hybrid drive unit described therein comprises at least one, preferably two, selectable clutch devices, of which one acts as a separating clutch and the other as a start-up clutch.
Therefore, there has been a long felt need in the art to provide and configure a drive train for a combined power transmission and drive unit for the application in a hybrid system of the type mentioned above such that it is additionally suitable, based on possibility, for the already available and required transmission oil pump, free of an ancillary pump, to avoid the disadvantages mentioned above. In this way, the solution according to the invention shall be characterized above all by emergency operation properties, in which the selectable clutch device transmits torque during an emergency operation and further enables smooth opening of the selectable clutch device during electric driving.